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Public Functions

Detailed Description

The QSemaphore class provides a general counting semaphore.

A semaphore is a generalization of a mutex. While a mutex can only be locked once, it's possible to acquire a semaphore multiple times. Semaphores are typically used to protect a certain number of identical resources.

Semaphores support two fundamental operations, acquire() and release():

acquire(n) tries to acquire n resources. If there aren't that many resources available, the call will block until this is the case.

release(n) releases n resources.

There's also a tryAcquire() function that returns immediately if it cannot acquire the resources, and an available() function that returns the number of available resources at any time.

A typical application of semaphores is for controlling access to a circular buffer shared by a producer thread and a consumer thread. The Semaphores example shows how to use QSemaphore to solve that problem.

A non-computing example of a semaphore would be dining at a restaurant. A semaphore is initialized with the number of chairs in the restaurant. As people arrive, they want a seat. As seats are filled, available() is decremented. As people leave, the available() is incremented, allowing more people to enter. If a party of 10 people want to be seated, but there are only 9 seats, those 10 people will wait, but a party of 4 people would be seated (taking the available seats to 5, making the party of 10 people wait longer).

1. Download the tools

Before you start developing, you'll need to visit the Downloads tab. Here you'll find downloads for the BlackBerry 10 Native SDK, BlackBerry 10 Device Simulator, and some other useful tools.

2. Try the sample apps

Now featuring a filter control, the Sample apps tab allows you to search for samples by name or by feature.

Select either the Core or Cascades radio buttons to display the samples relevant to you.

3. Educate yourself

The Documentation tab contains tons of examples, tutorials, and best practices to guide you along the path towards building an awesome app.

You can access all the documentation that you need in the left-hand navigation.

4. Start developing

The Reference tab is where you'll find essential details about how to use our APIs.

You can use the left-hand navigation to choose how you would like to browse the reference: by module, by topic, or alphabetically. If you have an idea of what you are looking for, start typing it in the Filter box.